1. Field of the Invention
The present invention relates to a field coil device for a brushless alternator for use in a vehicle and, more particularly, to a field coil holding device to be mounted on a fixed iron core in a brushless alternator for use in a vehicle.
2. Description of the Prior Art
A brushless motor for a vehicle is constituted, as is well known in the art, such that an armature core wound by an armature coil and a field core wound by a field coil are secured to brackets and disposed in a coaxial relationship, and magnetic poles are rotated between a pair of these fixed iron cores for deriving an AC output from the armature coil.
Heretofore, it is well known, in such brushless alternators as described above, that a cylindrical holder is secured to a fixed iron core by welding, or the like, to hold a spool for winding a field coil thereon instead of providing a field coil holding portion on the fixed iron core by engraving a recess at the periphery thereof, since many problems arise in the productivity and cost if such recessed portions are formed at the periphery of the fixed iron core. The disclosure of Japanese Utility Model Laid-open No. 60-135046 or Japanese Utility Model Laid-open No. 58-135081 is hereby incorporated as the prior art by reference.
Now referring to FIG. 1, there is shown a partial sectional view of a brushless alternator for a vehicle provided with a prior art field coil holder of the type mentioned above. A front bracket 1 and a rear bracket 2 of the brushless alternator are connected together by means of a connecting bolt (not shown). An armature core 3 is, then, interposed for mounting between inner peripheral faces of the abutting parts of the brackets 1 and 2, and an armature coil 4 is wound therearound. A rotor 6 is mounted on a rotary shaft 5 which is supported by the brackets 1 and 2 to form a unit body, and rotating magnetic poles 8 and 9 are juxtaposed in a teeth like relationship by interposing non magnetic rings 7 therebetween at the peripheral portion of the rotor 6. Further, a field coil 11 is disposed in a recessed portion 10 of the rotor 6 being formed at the inner peripheral part of the rotating magnetic poles 8 and 9. A field core 12 is secured to the rear bracket 2 and, then, a metallic cylindrical spool holder 14 is secured to the field core 12 by welding, or the like manner, for holding a field coil winding spool 13 made of insulating material.
FIG. 2 is a perspective view illustrating the field core 12 of the alternator shown in FIG. 1. FIG. 3 is a perspective view illustrating the metallic cylindrical spool holder 14 and FIG. 4 is a perspective view illustrating the field coil winding spool 13 wound by the field coil 11. Referring firstly to FIG. 2, a pair of through holes 16 are provided at an outer periphery of the field core 12 in the axial direction thereof for taking out lead wires 15 of the field coil 11. The lead wires 15 of the field coil 11 are then led through these through holes 16 to a power source for power supply.
Since the cylindrical field coil holder of the prior art brushless alternator is provided by welding, or the like method, the metallic cylindrical spool holder 14 of FIG. 3 is welded to the field core 12 of FIG. 2 for holding the field coil winding spool 13. Therefore, a comparatively high dimensional accuracy is required at the engaging parts of the field core 12 and the metallic cylindrical spool holder 14, and also there are too many necessary items to assemble. These requirements have resulted in a high cost in manufacturing. In order to provide the through holes 16 at the periphery of the field core 12, many manufacturing steps are required in machining with respect to the field core 12. In addition to this, there is a problem in winding of the field coil 11 since the winding of the field coil 11 has to be done after the field coil winding spool 13 has been retained at the field core 12 by the metallic cylindrical spool holder 14.
It is, therefore, an object of this invention to provide a simple and inexpensive field coil holding device by eliminating the metallic cylindrical spool holder to solve the problems encountered in the prior art brushless alternator.